The hardest part of using CriticCode (or any interview-prep exercise) is writing a good challenge statement. A weak statement tends to produce safe, boring answers from every candidate, because the candidate can only respond to what was actually written down. A strong statement puts the candidate on a specific, unfamiliar problem with room to reason in front of you. Most of the skill in running a tool like this lives in the gap between those two shapes, which makes it worth spending time on before the first invitation goes out.

Here's the shape of a challenge that works, and three worked examples.

The three things a good challenge has

A specific, non-generic scenario. Not "design a URL shortener". Not "build a todo app". Both of those have pre-computed answers sitting on the public internet. The candidate's response to them will be indistinguishable from every other candidate's response, and indistinguishable from what an AI would produce if you pasted the prompt in cold. Instead: describe a situation with real constraints. "We run a scheduling tool for restaurants. We're seeing reservations get double-booked at peak hours because our write path isn't serialised. Here's the current architecture. What would you change?" Specificity kills rehearsal.

An explicit ambiguity the candidate has to resolve. The best challenges don't have one right answer. They have several defensible answers, and the interesting part is watching the candidate pick one. That means leaving something genuinely unclear: which layer to modify, which trade-off to accept, which stakeholder to side with. If the statement pre-answers every obvious question, what you get back tends to read as compliance with the prompt rather than reasoning about the problem.

A reason this specific company would ask it. The challenge should feel like it came from your world, not from a general pool of interview questions. This matters for two reasons: it's harder to Google, and it signals to the candidate that you care about the specific thing you're testing. Both make the answers you get back more honest.

Three worked examples

Backend engineer, mid-level

Weak: "Design a rate limiter."
Strong: "Our public API exposes an endpoint that free-tier users hit to download their own data. We're seeing a handful of accounts hammer it continuously. Their scripts clearly haven't got backoff. The support cost of handling the complaints is starting to annoy us. What would you do, and what would you specifically not do? Assume Rails, Postgres, Redis."

The second version anchors to a real operational frustration, forces a choice between several valid approaches (IP limiting, token bucket, account-level throttling, support-side communication), and rules out a few generic answers by specifying the stack.

Frontend engineer, senior

Weak: "Build a searchable list component."
Strong: "We have a list of up to ~50,000 rows that our ops team scrolls through hundreds of times a day. They've complained that the search is slow and that the rows jump around when they type. Given the constraints (React, no custom infra team, ops team not technical enough to wait for a backend rewrite), what's the cheapest change you can propose that fixes the worst of this within a week? What would you push back for more time on?"

The second version forces a trade-off between scope, technical purity, and timeline. You will find out immediately whether the candidate picks the cheapest-right-thing or the most-elegant-thing. Both are valid, but knowing which one they pick tells you a lot about how they'll behave on your team.

Engineering manager, first-line

Weak: "Describe your management philosophy."
Strong: "You've just taken over a team of five. Two of the five were external hires within the last six months; one has been around for four years and is considered a top performer, but two other engineers on the team have told you independently that they find her difficult to work with. The team ships slowly. Your skip-level wants you to 'fix the velocity problem' in your first quarter. Walk me through your first thirty days."

The second version has four or five competing pressures embedded in it and lets the candidate tell you which they prioritise. Generic answers fall off immediately. The answer is going to be specific, unrehearsed, and revealing.

One thing worth avoiding

A pattern worth catching early is writing a challenge that quietly rewards the candidate for guessing your internal architecture. A good challenge gives the candidate enough information to reason, and then lets them reason. If the highest-scoring responses mostly turn out to be the ones that happened to match how your team currently does things, the exercise is measuring proximity-to-gossip rather than judgement.

The goal of a good challenge, in the end, is to produce an answer you can actually have a conversation about. If reading the response leaves you with a list of follow-up questions you're excited to ask, the challenge has done its job.